The paper presents a critical review of the notion of the factor of safety, a commonly used concept in geotechnical practice to prevent the failure of a certain structure. This concept reflects the measure of the reliability of a given geotechnical design and is related to the lack of confidence in the design process. The paper argues that, in spite of the fact that it is a widely adopted design tool, there are several shortcomings in using this concept indiscriminately because of problems associated with the definition of the safety factor itself, the determination of the stress state in the foundation, the assumed stress paths under loading and the use of the failure criterion. As a result, the calculated factor of safety may not be a correct reflection of the real in situ situation and thus, may lead to unsafe designs. A discussion on practical consequences and associated risks is presented in relation to slope stability analyses and recommendations are proposed for safer designs.
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